On Thu, Nov 30, 2023 at 05:07:40PM -0300, André Almeida wrote: > From: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx> > > Specify how the atomic state is maintained between userspace and > kernel, plus the special case for async flips. > > Signed-off-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx> > Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx> > --- > > This is a standalone patch from the following serie, the other patches are > already merged: > https://lore.kernel.org/lkml/20231122161941.320564-1-andrealmeid@xxxxxxxxxx/ > > Documentation/gpu/drm-uapi.rst | 47 ++++++++++++++++++++++++++++++++++ > 1 file changed, 47 insertions(+) > > diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst > index 370d820be248..d0693f902a5c 100644 > --- a/Documentation/gpu/drm-uapi.rst > +++ b/Documentation/gpu/drm-uapi.rst > @@ -570,3 +570,50 @@ dma-buf interoperability > > Please see Documentation/userspace-api/dma-buf-alloc-exchange.rst for > information on how dma-buf is integrated and exposed within DRM. > + > +KMS atomic state > +================ > + > +An atomic commit can change multiple KMS properties in an atomic fashion, > +without ever applying intermediate or partial state changes. Either the whole > +commit succeeds or fails, and it will never be applied partially. This is the > +fundamental improvement of the atomic API over the older non-atomic API which is > +referred to as the "legacy API". Applying intermediate state could unexpectedly > +fail, cause visible glitches, or delay reaching the final state. > + > +An atomic commit can be flagged with DRM_MODE_ATOMIC_TEST_ONLY, which means the > +complete state change is validated but not applied. Userspace should use this > +flag to validate any state change before asking to apply it. If validation fails > +for any reason, userspace should attempt to fall back to another, perhaps > +simpler, final state. This allows userspace to probe for various configurations > +without causing visible glitches on screen and without the need to undo a > +probing change. > + > +The changes recorded in an atomic commit apply on top the current KMS state in > +the kernel. Hence, the complete new KMS state is the complete old KMS state with > +the committed property settings done on top. The kernel will try to avoid > +no-operation changes, so it is safe for userspace to send redundant property > +settings. However, not every situation allows for no-op changes, due to the > +need to acquire locks for some attributes. Userspace needs to be aware that some > +redundant information might result in oversynchronization issues. No-operation > +changes do not count towards actually needed changes, e.g. setting MODE_ID to a > +different blob with identical contents as the current KMS state shall not be a > +modeset on its own. As a special exception for VRR needs, explicitly setting > +FB_ID to its current value is not a no-op. > + > +A "modeset" is a change in KMS state that might enable, disable, or temporarily > +disrupt the emitted video signal, possibly causing visible glitches on screen. A > +modeset may also take considerably more time to complete than other kinds of > +changes, and the video sink might also need time to adapt to the new signal > +properties. Therefore a modeset must be explicitly allowed with the flag > +DRM_MODE_ATOMIC_ALLOW_MODESET. This in combination with > +DRM_MODE_ATOMIC_TEST_ONLY allows userspace to determine if a state change is > +likely to cause visible disruption on screen and avoid such changes when end > +users do not expect them. > + > +An atomic commit with the flag DRM_MODE_PAGE_FLIP_ASYNC is allowed to > +effectively change only the FB_ID property on any planes. No-operation changes > +are ignored as always. Changing any other property will cause the commit to be > +rejected. Each driver may relax this restriction if they have guarantees that > +such property change doesn't cause modesets. Userspace can use TEST_ONLY commits > +to query the driver about this. The wording LGTM, thanks! Reviewed-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx> -- An old man doll... just what I always wanted! - Clara
Attachment:
signature.asc
Description: PGP signature
